How to set up the intercom function between a Cisco phone and Frepbx

How to set up the intercom function between a Cisco phone and a Frepbx phone. The function itself is configured on the server, but I can’t figure out how to assign an intercom line to Cisco and tie it to the server.
Please help.

What kind of Cisco phone? What Version of Freepbx? Are you using Endpoint Manager?

it is up to the phone to provide auto-answer if asked to by a SIP message, every phone might or might not be able to do that, but the setup will always be dependent on the phones provisioning, so ask the Cisco community perhaps?

(Caveate, Cisco phone might actually be Cisco (but you need to know the software load), Linksys, Sipura or generic Chinese reference design)